I'm currently a student and have had a different preceptor in all five of my clinical rotations. Personally, I get the best experience when my preceptor has me do everything, including charting/orders/etc. and then she reviews it with me. I would do my assessment, pass meds (as a student, I always asked my preceptor first if she was okay with me giving meds by myself. I don't have access to the Pyxis, though, so any controlled substances were given to me by my preceptor), and chart my findings. My preceptor would then go in and do her own assessment and look over my charting and then we would discuss it. I would give report to the NP/MD as needed and she would help fill in any gaps that I missed. If any orders were given, I put them into the computer (although if it were a verbal/phone order, I'd have my preceptor write the order down as I cannot take verbal orders as a student). I'd also answer any call lights.
This worked for me the best because I was able to get a true sense of what a typical day is for a nurse. Most of my preceptors would have me do all of the patient care/assessment charting, but they would do the orders. Once I was taught how to do orders and was responsible for them, my days were a lot more hectic and probably a lot more realistic.
I'd ask your student how he/she learns best. Does she want to follow you for a day first before jumping in, or does she want to jump right in? Also, and maybe I'm just weird, I don't like having my preceptor standing over my shoulder while I'm doing my assessment. It just makes me nervous and I feel too much like a student. When I go into the patient's room without my preceptor, I feel much more independent and I act more like a nurse. If a patient has a question that I don't know about, I just tell them that I will have my preceptor come in and answer their question. If I have to do a Foley/IV/etc., my preceptor comes in with me and makes sure that I am doing everything correctly.
One of my preceptors quizzed me each day on the basics of the meds that I was passing and any side effects. When I was on the Med/Onc floor, she would quiz me on the patho of the diagnoses we saw and had me study up on anything that I wasn't familiar with. That was really helpful. She also taught me to always look things up for myself and not rely on another nurse (what if that nurse doesn't have the correct information?).
So all-in-all, I would ask your student what he/she prefers, but for me, being independent and doing as much as possible works the best.